1. Field of the Invention
The present invention relates to a backup power supply of a power supply circuit used for an image forming apparatus.
2. Description of the Background Art
In general, when supply of electric power to a system abruptly stops due to an interruption of power supply for example, it is desirable to stably stop the system while preventing any malfunction for example of the system.
Regarding personal computers for example, when a circuit breaker abruptly trips due to an interruption of power supply for example, generally a so-called backup power supply that detects the breaker's tripping to temporality supply electric power for continuing the power supply is used to prevent data for example that has been being generated from breaking.
In particular, in recent years, a backup power supply that uses an uninterruptible power supply (UPS) to prevent loss of memory contents or a malfunction of a personal computer for example has been of great interest. Japanese Patent Laying-Open Nos. 01-129725 and 09-200974 each disclose a configuration having, in addition to a power supply circuit used in a normal state, a backup power supply circuit that can temporarily supply electric power in an emergency state, for example, when an interruption of power supply occurs, for continuing supply of desired electric power to a certain extent in such an emergency state as the interruption.
The disclosed configuration, however, includes, in addition to the normal power supply circuit, the backup power supply circuit, a storage battery for example, used when an interruption occurs, which means that an additional dedicated circuit is necessary, resulting in a problem in terms of the occupied area and cost.
In particular, in these days, most image forming apparatuses, printers for example, are configured to have various functions including a CPU (central processing unit) and accordingly require a larger area, and thus it is an important issue to reduce the area.